The present invention relates to a valve, able to perform multiple functions and applicable to systems which are subject to intense variations in pressure such as boilers which are exposed to frequent stoppages with cooling, and constitutes an improvement to the device for self-priming, under backpressure conditions, vibration pumps, which is covered by Industrial Utility Model No. 0,215,741 filed on Mar. 3, 1989 in the name of the Applicants of the present application.
The above mentioned device has proved to be very effective for re-priming vibration pumps under overpressure conditions, but has been unable to successfully resolve a new problem which has arisen when vibrations pumps are used for supplying large-size boilers, such as those of multiple steam generators for stream-cleaners and for irons. In fact, what happens is that when these boilers, after a working cycle, are allowed to cool, the pressure in the closed space present above the water level, which is intended for storage of the steam, passes from a value substantially higher (by a few bars) than atmospheric pressure to a value which is lower than atmospheric pressure, i.e. this space is subject to a negative pressure. Since the apparatus which contain these boilers are generally provided with valves which prevent the steam from escaping, except when this is required by the operator, it is impossible to draw any compensating air from the external environment. Consequently, if a boiler is provided, in the supply circuit, with a pump self-priming device, as described in the above mentioned utility model, the negative pressure inside the boiler draws water from the hydraulic supply circuit to the point where it completely fills the boiler, resulting in serious malfunctioning of said boiler during subsequent use since, instead of producing dry steam immediately, initially the boiler emits mixtures of water and steam which may be harmful or dangerous.
It is therefore necessary to use a valve which operates so that it not only releases air in order to re-prime the pump, but also allows a gradual intake of air to the boiler to be supplied when the latter is subject to a negative pressure.
The present invention is intended for this purpose and consists of a device which performs the multiple functions of self-priming of the pump, compensation of negative pressure inside the boiler and protection of the latter against overpressure, said device comprising a non-return valve and an air release valve situated upstream of the non-return valve, characterized in that a discharge pipe of the air release valve terminates above the surface of the water contained in a tank for reserve of supply water, in that this valve, in addition to opening completely in order to release the air externally in the event of re-priming of the pump, is also able to admit a flow of air from the outside towards the boiler so as to allow compensation of the negative pressure in said boiler without drawing water from the tank.
In addition, the device according to the invention is characterized in that an externally discharging safety valve is installed downstream of the non-return valve.
Preferably, the safety valve discharges into the same discharge pipe as the air release valve.
In particular, the valve, which opens completely in order to release the air, in the event of re-priming of a pump, and is also able to admit a flow of air from the outside to the boiler, consists of a plug provided at a first end located towards the central axis of the device with a recess which favours the through-flow of air.
More particularly, this recess is formed by a cylindrical cavity coaxial with the plug, directed towards the inside of the device and provided with at least one incision connecting the cavity to the periphery of the plug.
Preferably, the incisions are two in number.
More preferably, the incisions are three in number.
In particular, the safety valve, which is installed downstream of the non-return valve, is formed by a cylindrical seat which is provided with a narrow hole communicating with the said downstream zone and kept closed by a ball pushed by a spring calibrated in accordance with a safety pressure.
The features of the present invention will be defined in particular in the claims forming the conclusive portion of the description.
However, other features and advantages thereof will emerge from the following detailed description of a preferred and non-limiting embodiment thereof, with reference to the enclosed drawings, in which:
FIG. 1 shows a cross-sectional side view of an embodiment of the invention;
FIG. 2 shows a perspective view of a plug present in the valve for releasing air and compensating for the negative pressure of the device according to the invention;
FIG. 3 shows a cross-sectional view along the line 3xe2x80x943 of FIG. 2; and
FIG. 4 shows an example of a possible application of the device according to the invention to a large-size boiler for generating steam for domestic use.